baerwald



Oct. 4, 1955 H. G. BAERWALD TWISTER-TYPE ELECTROMECHANICAL DEVICE 2 Sheets-Sheet 1 Filed May 22. 1951 INVENTOR HANS G BAERWALD Z z AT RNEY Oct 1955 H. G. BAERWALD 2,719,928

TWISTER-TYPEI ELECTROMECHANICAL DEVICE Filed May 22, 1951 2 Sheets-Sheet 2 4| 43 42 4o v 36 31 bMPLlFlEF J 32 44 47 5 Q 30 as c AMPLIFIER -O 0 FIG. 2

DIRECTION OF SIGNAL FIELDS 35 '1 wk F FIG.3

INVENTOR. HANS G. BAERWALD AT RNEY United States Patent TWISTER-TYPE ELECTRUMECHANICAL DEVICE Hans G. Baerwald, Cleveland Heights, Ohio, assignor, by mesne assignments, to Clevite Corporation, Cleveland, Ohio, a corporation of Ohio Application May 22, 1951, Serial No. 227,571

8 Claims. (Cl. 310-81) The present invention relates to twister-type electromechanical devices and, specifically, to a device. which, when twisted, mechanically will generate electrical energy or, when electrical energy is applied thereto, will twist mechanically.

Electromechanical transducers, per se,. are well known in the art and have found many uses in microphones, phonograph pickups, etc. Some of these devices comprise a piezoelectric material and the expansion properties thereof, when a voltage is applied to electrodes on the device, are utilized. Others of the devices. utilize some arrangement to stress the material mechanically so that the expansion properties of the material causes a voltage to be generated. However, for most purposes, it has been found desirable to utilize a sandwich of two such elements to provide, for example, a bending action under an applied voltage or to generate a voltage in response to a bending action. Still other such devices operate to provide a voltage in response to a twisting action or provide a twisting action in response to a voltage. These devices are generally comprised of a sandwich of two electromechanically responsive plates in which the mechanical action involved is a shear in the face of each of the plates. When a sandwich of two such plates is utilized with a shear action of opposite sense in each. of, the plates, a so-called twister device is provided in a manner which, per se, is well understood by those skilled in the art.

However, in recent years ceramic electromechanical transducers have come into an extensive amount of use. Such transducers are generally comprised of a fired ceramic material which is. comprised mainly of barium titanate, although in some cases, the material may have added thereto a few weight percent of some metal oxide in order to provide some particular operating characteristic; Generally speaking, there are always fractional percentages of other materials present as impurities in the barium titanate which is used to make such. transducers. Transducers which are made of such ceramic materialsv are effective to change mechanical energy into electrical energy or to change electrical energy into mechanical energy or both. They also have found a considerable amountv of. use as the transducing devices in microphones, phonograph pickups, devices for introducing sound energy into a liquid medium, devices for producing electrical energy from sound energy in a liquid medium, etc. Several such ceramic transducers. are described and. claimed in United States Letters Patent. No. 2,486,560 granted on November 1, 1949, on an. application filed September 20, 1946, by Robert B. Gray.

While ceramic transducers of the type here under consideration have. found some use. in devices where a continuous unidirectional bias. voltage is applied while the transducer is in operation, it is the general practice, to cause the. material of such transducersto have a remanent polarization which renders the provision of the continuous unidirectional bias voltage during the operation of the device unnecessary. The ceramic materials of the type here under consideration are caused to have aremanent polarization by subjecting the material to a highintensity electric field at some time during the manufacturing process of the device. This polarizing process is done after the material has been fired and is usually done after suitable electrodes have been applied to surfaces of the material. It is usually necessary or desirable to apply a polarizing field of the order of 75,000 volts per inch to the material at ambient room temperatures, al though it is possible to reduce this voltage gradient requirement by about half if the material being polarized is maintained at a temperature near, and preferably just below, its Curie point. The Curie point of barium titanate is around C. The ceramic materials of the type discussed hereinabove, which in general have electromechanical responses of very substantial magnitudes involving deformations in various modes including a shear mode, may be designated as permanently polarizable titanate-type polycrystalline ceramic materials.

Many of the barium titanate ceramic materials here under consideration have a relatively strong mutual coupling action between an electric signal field at right angles to the direction of remanent polarization and a mechanical shear in the plane which includes the direction of polarization and the electric field just mentioned. Specifically, if an electric signal field is applied to the material with the proper direction, the ceramic material will be subjected to a mechanical shear; and, conversely, if the material is subjected to a mechanical shear of the proper orientation, an electric signal field will result in the material, which signal field can be utilized to derive electrical energy from the material. The mutual coupling coefiicient here under consideration has a value of about 0.4 for a properly polarized ceramic material of barium titanate. It would be very desirable, therefore, to provide a twister device made up of a sandwich of two shear plates of such ceramic material.

Furthermore, the ceramic material here under consideration has another very desirable property in that two shear plates can be ceramically bonded together in such a way as to provide what is essentially a unitary mechanical structure. As will be brought out in more detail hereafter, operating electrodes must be provided for such a twister device and, if the direction of polarization is opposite in the two shear plates, the most closely adjacent opposing electrodes upon the two plates of the sandwich involved can advantageously be of the same potential. Where, however, the two plates are bonded together ceramically as mentioned above, it is very difiicult to provide remanent polarizations of opposite directions in the two plates, for the reason that the heating necessary ceramically to bond the two plates together is generally elfective to destroy any remanent polarization of the plates. On the other hand, if in such a unitary structure the. polarization is in the same direction of each of the plates, the signal fields of the two plates must be substantially opposite in opposing portions of the two plates of the sandwich during the operation of the device. This requirement cannot be fulfilled in the ordinary sandwich structure without the introduction of very strong dielectric leakage fields between opposing electrodes onthe two plates, and this is very undesirable because in such. an arrangement most of the electric energy of the device is not associated with the desired mutual coupling action between the signal field in the material and the mechanical shear mentioned above.

It would be very desirable, therefore, to provide a twister device of the general nature here under consideration in which the electromechanically sensitive material involved can be ceramically bonded and prepolarized and still have the undesired shunting'action of adjacent electrodes on the two plates of the sandwich reduced to a minimum. By the present invention, applicant has provided such a device.

It is an object of the invention to provide an improved electromechanical twister device.

It is still another object of the invention to provide a twister-type electromechanical device which effectively comprises a sandwich of two elements mechanically connected together and one which can be prepolarized after the two elements have been bonded together.

It is still another object of the invention to provide a twister-type electromechanically sensitive device which is easy to manufacture, using ceramic materials, in that all of the ceramic materials involved may be fired together as one unit.

It is still another object of the invention to provide an improved electromechanical twister device which has a very high coupling efficiency in its desired mode of action.

In accordance with the invention, a twister-type electromechanical device comprises two superimposed plates of dielectric material having a relatively high dielectric constant, each of the plates having a remanent polarization in substantially the same direction and a mutual coupling action as between an electric signal field substantially in the plane of the plate normal to the direction of polarization and a mechanical shear substantially in the plane of the plate. The device also comprises a center layer of material of relatively low dielectric constant between the above-mentioned plates which is effective to connect the plates mechanically. Electrodes are provided which are effectively spaced in the above-mentioned signal field direction in each of the above-mentioned plates. There is also included a means for effectively providing, during operation of the device, potential differences between the above-mentioned electrodes of the plates corresponding to signal fields between the electrodes, the directions of which are substantially opposite in opposing portions of the plates. By this arrangement, a twisting action of the device can be converted into electrical energy, or vice versa, and an undue shunting action between an electrode of one of the plates and electrodes of the other plates is obviated.

As used in this specification. the terms relatively high dielectric constant and relatively low dielectric constant are always used together and are intended to refer to dielectric constants having a large difference in magnitude. This difference in magnitude should be at least and preferably should be 100 or more.

For a better understanding of the present invention, together with other and further objects thereof, reference is had to the following description taken in connection with the accompanying drawings, and its scope will be pointed out in the appended claims.

In the drawings, Fig. l illustrates an embodiment of the invention utilized as the electromechanical device of a phonograph pickup or a record cutter; Fig. 2 illustrates certain additional features of the Fig. 1 device; while Fig. 3 is an illustration which is primarily useful to show how the device of the invention should be proportioned for various applications.

Referring now more particularly to 1, there is there shown a twister-type electromechanical device in accordance with the invention which has been indicated generally by the reference numeral 10. A preferred embodiment of the invention involves the use of the device 10 as the electromechanically sensitive element of a phonograph pickup or as the electromechanically sensitive element of a phonograph record cutter and the device of Fig. 1 can be used for either purpose. For the moment. however, the illustration of Fig. 1 will be considered to apply only to a phonograph pickup device. Thus Fig. 1 comprises a turntable 11 driven by an electric motor 12 having electrical leads 13 and A phonograph record 16 is shown in place on the turntable 11 which is adapted to be rotated by the motor 12. The device also includes an arm 17 which is pivoted within the structure 18 in order to allow a needle 19 to follow grooves in the phonograph record 16 in a manner which is well understood, per se, by those skilled in the art.

The electromechanical device 10 is held within a housing 20 in the arm 17 by means of a bracket 21 which in turn is affixed to the housing 20 by means of screws 22, 23. One end of the device 10 is rigidly clamped to one arm of the bracket 21 by means of a clamp 24. To the other end of the device 10 is attached a clamp 25 to which is affixed a pivot 26 which operates in a bearing in the racket 21. The needle 19 is rigidly fastened to the structure including the clamp 25 and the pivot 26 so that to-and-fro motions of the needle, in directions illustrated by the double-headed arrow 27, which are caused by the record member 16 are effective to provide a twisting action of the electromechanical device 10. Clamps 24 and 25 are preferably of a non-conducting material in order that they will not interfere with the electrical characteristics of device 10 in a manner which will be apparent from the detailed description of device 10, to be given hereinafter.

Alternatively, the device just described may be considered to be a record cutter in which the to-and-fro movements of the needle 19 are effective to cut a record into the member 16 in a manner which, per se, is well understood by those skilled in the art. However, the proportioning of the device 10 must be quite different for these two types of operation and the manner in which the device should be proportioned in each case will be described in detail hereinafter.

The device 10 of Fig. l is a twister-type electromechanical device and comprises two superimposed plates 30, 31 of dielectric material having a relatively high dielectric constant. Each of the plates 30 and 31 has a remanent polarization in substantially the same direction. In the device illustrated, the direction of polarization is in the length direction of the plates. Under these conditions, and utilizing one of the ceramic materials mentioned above which has been properly polarized in the manner described above, there exists a mutual coupling action as between an electric signal field substantially in the plane of the plate normal to the direction of polarization and a mechanical shear substantially in the plane of the plate. Since, as mentioned hereinabove, the plane of the shear includes the direction of polarization, the direction of polarization must be in substantially the plane of each plate, whether or not that direction coincides with the length direction of the plate.

The device 10 also comprises a center layer 32 of a material of relatively low dielectric constant between the plates 30 and 31. This center layer is effective to connect the plates 30 and 31 mechanically and is preferably a ceramic material which has been fired between the plates 30, 31 so as to connect the plates mechanically in a unitary structure.

Electrodes 35, 36, 37, and 38 are provided for the device 10 and electrodes 36 and 37 are effectively spaced in the above-mentioned signal-field direction in plate 31. Specifically, electrode 36 is provided along one edge of the plate 31 and electrode 37 is provided on the other edge of the plate 31. The electrodes 36 and 37 extend for the entire length of the plate. Similarly electrodes and 38 are provided for the plate 30.

Reference is now made to Fig. 2 where an end view of the device 10 of Fig. l is illustrated and similar circuit elements have identical reference numerals in the two figures. The two plates 30 and 31 are preferably comprised of any of the barium titanate materials mentioned above which have a strong mutual coupling action as between an electric field in the plane of the plate normal to the direction of polarization and a mechanical shear substantially in the plane of the plate. Such material also has a relatively high dielectric constant. The center layer 32 is preferably comprised of a similar ceramic material but one having a relatively low dielectric constant and is not required tobe a: polarizable materialor, in fact, one having any electromechanical sensitivity. The plates 30 and 31 are'preferably fired with the center layer 32 between the plates in order to provide a strong ceramic bonding of the two plates 30 and 31 and thus to provide what is essentially a mechanically integral structure. Such a structure can be polarized in the length direction by means of electrodes applied to the end surfaces of the structure before the electrodes 35, 36, 37,

38 are affixed thereto. Alternatively, it is sometimes desirable to polarize the two plates and 31 without afiixing polarizing electrodes thereto and this can be done by providing any suitable arrangement by which an intimate electrical contact can be made to the ends of plates 30 and 31 and thus effectively provide temporary electrodes for polarizing purposes. If polarizing electrodes are actually applied to the ends of plates 30 and 31, it is necessary that they be removed thereafter because otherwise they would have the effect of short circuiting the signal-field electrodes 35, 36, 37, and 38.

It will be understood that, while a ceramic bonding of the plates is described above, other methods may be utilized. Thusplates 30 and 31 may each be atfixed to center layer 32 by means of cement.

The remaining portion of Fig. 2 is provided for the purpose of illustrating, in conjunction with Fig, 1, the use of the element 10 either as a phonograph pickup device or as a record cutter. Thus Fig. 2 includes a microphone 40 which may be coupled through an amplifier 41, a switch 42, and leads 43 and 44 to the electrodes of the device 10. Specifically, lead 44 is connected to electrodes 36 and 38 and lead 43 is connected to electrodes and 37. Alternatively, the leads 43- and 44 may be connected to a loudspeaker 46 through an amplifier 47 and the switch 42 when the switch 42 is in the dotted position as shown in Fig. 2.

The operation of the device of Figs. 1 and 2 will first be explained as a record cutter which requires that the switch 42 be in the full-line position illustrated in Fig. 2. Under these conditions, it is assumed that the motor 12 is effective to drive a blank record disk 16 and that the arm 17 is suitably tracked over a spiral record path on the face of the record blank 16 by some suitable means (not shown). The sounds to be recorded are picked up by the microphone (Fig. 2) and amplified by the amplifier 41 and applied to the electrodes of the device 10. These signal voltages cause a twisting action of the device 10 (Fig. 1) which, since one end of the device is clamped by the member 24, is effective to move the needle 19 to and fro in the direction generally indicated by the double arrow 27 and in a manner corresponding to the signals to be recorded. These to-and-fro movements of the needle 19 actually out corresponding portions of the member 16 to provide a permanent record of the sound signals at microphone 40.

in considering the operation of the device of Figs. 1 and 2 asa phonograph pickup device, it will be assumed that a record 16 to be reproduced is placed on the turntable 11 and that it is driven by the motor 12. It will also be assumed that the switch 42 of Fig; 2 is in its dotted position. Under these conditions, the recording in the record grooves is effective to cause a to-and-fro motion of the needle 19, again as generally representedby the arrow 27. These motions of the needle apply twisting motions to the device 10- and are effective to provide at. the electrodes of device 10 signal voltages corresponding to the record being produced. These signal voltages are transmitted by means of leads 43 and 44 (Fig. 2) through the switch 42 to amplifier 47 wherein they are amplified and after which they are reproduced by the loudspeaker 46.

During the operation of the device 10, either as a phonograph pickup or as a record cutter, potential differences between electrodes of plates 30 and 31 corresponding to signal fields between the electrodes are provided. These signal-field directions are substantially opposite in opposing portions of the two plates 30 and 3.1. Thus potential differences are provided between electrodes 36 and 37 of'plate. 31 and electrodes 35 and 38 of plate 30; these potential differences correspond to signal fields between the electrodes of the respective plates, and the direction of the signal field between electrodes 36 and 37 of plate 31 is opposite to the direction of the signal field between electrodes 35 and 38 of plate 30.

it will be apparent that, during either of the operations described above, the requirements for potential differences between the electrodes of plates 30 and 31 are such that comparatively high potential differences exist also between an electrode of one of the plates and an adjacent electrode of the other of the plates. For example, the full voltage between leads 43 and 44 appears between electrodes 35 and 36 and between electrodes 37 and 38. if only the material of plates 30 and 31 were present in the structure, these last-named voltages would have a very deleterious effect upon the operation for the reason that a very undesirable shunting action would be provided in the device. It is primarily for the purpose of obviating this undesired shunting coupling action that the center layer 32 of relatively low dielectric constant material is provided.

It is also apparent that, when used as a record cutter, the device 10 is a twister-type electromechanical device for converting electrical energy into mechanical energy. Conversely,v it is apparent that, when used as a phonograph pickup, the device 10 is a twister-type electromechanical device for converting mechanical energy into electrical energy. It will be understood that the various elements of device 10 must be proportioned in accordance with the use to which the device is to be put, and the proportioning of the device 10 for a phonograph pickup, for example, is entirely different from that required for a record cutter.

Reference is now made to Fig. 3 for a consideration of the manner in which the element 10 should be proportioned when used in devices of various types. In Fig. 3, components which are similar to those of Figs. 1 and 2 have identical reference numerals. The electrodes 35, 36, 37, and 38 in Fig. 3, however, have been shown as extending over the edge surfaces of the plates 30 and 3-1 and. symbols representing the various dimensions of the structure have been added in order that the various general characteristics of the structure may be set forth hereinafter. These are:

Where S is the torsional or angular compliance, where the dimensional reference characters correspond to those illustrated in Fig. 3, and where the parameter G is the shear modulus in Newtons per meters square for the plates 30 and 31 as well as approximately for the plate 32. For most of the titanate materials mentioned above, the shear modulus G is approximately equal to 4-10 Newtons per meters square. The magnitude of the shear modulus of the center layer relative to that of the plates is not critical for efiicient design and operation of the device, as it carries relatively minor stresses, but it should not deviate too much from one; that is, it should be between about one half. and two.

2. The active or internal capacity C present at the terminals 43, 44 of the device of Fig. 3 connected as illustrated in Figs. 1 and 2 is approximately equal to:

21d, ba+da farads where so is the vacuum dielectric constant, 0.884'l0- farads per meter, and Ka is the numerical dielectric conradians per Newton meter c K f farads where K1 is the numerical dielectric constant of the low dielectric or passive dielectric material of center layer 32.

4. The open circuit voltage for an applied torque, under the condition that CL=0, is:

S volt; meters per Newton or 77468 6 meters square per coulomb where ks is the electromechanical coupling coefficient for the shear mode for the material of plates 30 and 31 and where '17 is the electromechanical coupling efficiency of the structure.

The parameter ks is approximately 0.4 for many of the ceramic materials mentioned above. The effective coupling coefficient kefi of the torque mode of the structure as a whole is:

A mutual elasto-dielectric self energy 77' /(elastic self energy)(dielectric self energy) 5. The equivalent resonance moment of inertia Ii of the structure 10 of Fig. 3 is:

Newton meter second square per radian If p represents the density of the material of the plates 30, 31 and, approximately, of the layer 32,

is the velocity of propagation of elastic shear. The equivalent resonance moment of inertia It is defined by the condition that, in combination with the torsional compliance S, it will result approximately in the correct value of the gravest mechanical resonance frequency of the structure 10 when clamped at rear end at 24 and free at the front end.

In the Fig. 1 arrangement where an external structure such as the stylus 19 and its associated clamp 25 is added to the device, it will be necessary to add to It the component Ie of the moment of inertia contributed by such external structure in order to obtain the entire efiective moment of inertia. In this case, Ii has to be replaced by PIe where the factor p decreases from when the ratio increases from 0 to In the device which has just been described, most of the electrical energy in the dielectric material is found in plates 39 and 31 between the electrodes associated with the respective plates. Also, for the twisting action involved in any of the devices described, the main electromechanically active shear stress in the dielectric material is found in the same region, and these factors provide a very decided improvement over prior-art twister elements using a sandwich of shear plates. Specifically and with special reference to Fig. 3, most of the electric signal field energy of plate 31, for example, is found in the plate 31 between the electrodes 36 and 37, and the main elastic stress energy in the electromechanically sensitive material of the plate 31, associated with the electromechanically active component of shear, is found in the same region. In the portions of the plates 30 and 31 between electrodes 35 and 36 and between electrodes 37 and 33, the signal fields are relatively weak due to the insulating action provided by the center layer of low dielectric material 32. Also, in these regions the shear stress in the dielectric material consists essentially of the electromechanically inactive stress component. If the ratio of width b to the thickness d of the structure is large compared to one, that is, at least about 2 /2, preferably 3 /2 or larger, this latter component is predominant in a minor part of the cross-sectional area only and thus contributes little to the overall elastic self energy. This feature, in conjunction with the fact that the electromechanically active shear component and electric si nal field are predominant in the same aforementioned regions, insures a high value of the coupling efficiency 1 which can thus be made larger than in the conventional wo-plate twister sandwiches mentioned earlier.

In designing a structure 10 for any particular application, there are certain relationships in addition to those set forth above between the various dimensional parameters which applicant has found to be preferable in selecting the dimensions. These are set forth hereinafter, although it will be understood that these relationships are not to be considered as limiting ones with reference to the invention but ones which in most cases will provide a better end result.

Specifically, for the sake of maintaining high coupling efficiency, it is generally desirable to provide a device in which the undesired or shunting capacitance C is much smaller than the useful capacitance C.

In order to provide this effect, the following formula should be followed:

Also, for the same purpose, the deleterious influence of end effects at clamps 24, 25 should be minimized; it is therefore generally desirable to provide a length 1 (Fig. 3) which is at least twice as great as the width b of the element.

Furthermore, for the same purpose and as explained previously, it is desirable that the ratio of the width b to the thickness d should have a value not less than 2 /2, preferably 3% or larger. The ratio of the overlap width bi of the electrodes 35, 36, 37, 38 to the overall thickness d of the element 10 is chosen such as to shield only those portions of the plates 30, 31 where the relative magnitude of the electromechanically active stress component is insignificant. It will thus be somewhat dependent on the aforementioned ratio b to d and lies preferably in the range 0.6, for b:d-2 /2, to 0.8, for b:d-5 or larger.

In some cases it may be found desirable to chose a different proportioning, and the dimension b may then even be equal to, or less than, the dimension 1.

While there have been described What are at present considered to be the preferred embodiments of this invention, it will be obvious to those skilled in the art that various changes and modifications may be made therein without departing from the invention, and it is, therefore, aimed in the appended claims to cover all such changes and modifications as fall Within the true spirit and scope of the invention.

What is claimed is:

l. A twister-type electromechanical device, comprising: two superimposed plates of dielectric material having a relatively high dielectric constant, each said plate having a remanent polarization in substantially the same direction in the plane of said plate and a mutual coupling action as between an electric signal field substantially in the plane of said plate normal to said direction of polarization and a mechanical shear; substantially in the plane of said plate; a center layer of material of rela tively low dielectric constant between said plates which is effective to connect said plates mechanically; electrode means, including at least two separate electrodes for each said plate effectively spaced in said signal-field direction along said respective plate, said electrodes for said two plates being effectively interconnected so that potential differences across said electrode means correspend to signal fields, substantially in said planes of said plates between said electrodes, the directions of which are substantially opposite in opposing portions of said two plates, and an undue shunting action between an electrode of one of said plates and an electrode of the other of said plates being obviated by said intervening center layer; and mechanical coupling means motion of which is associated with a twisting action of said device involving mechanical shears of opposite senses insaid two plates as constrained by said center layer; whereby any application of electrical energy to said electrode means to provide said potential differences thereacross causes said motion associated with said twisting action while any movement of said mechanical coupling means to provide said twisting action causes development of said potential differences across said electrode means.

2. A twister-type electromechanical device for converting electrical energy into mechanical energy, comprising: two superimposed plates of dielectric material having a relatively high dielectric constant, each said plate having a remanent polarization in substantially the same direction in the plane of said plate and being effective under the influence of' an electric signal field substantially in the plane of said plate normal tosaid direction. of polarization to develop a mechanical shear in the plane of said plate; a center layer of material of relatively low dielectric constant between said plates which is effective to connect said plates mechanically; electrode means, including at least two separate electrodes for each said plate effectively spaced in said signahfield' direction along said respective plate, said electrodes for said two" plates being effectively interconnected so that potential differences across said electrode means correspond to signal fields, substantially in said planes of said plates between said electrodes, the directions of which are substantially opposite in opposing portions of said two plates, andan undue shunting action between an electrode. of one of said plates and an electrode of the other of said plates being obviated by said intervening center layer; mechanical coupling means motion of which is associated with a twisting action of said device involving mechanical shears of opposite senses in said two plates as constrained by said center layer; and means for applying electrical energy to said electrode means to provide said potential differences thereacross, whereby such applied electrical energy is converted into said twisting action of said device, resulting in said associated motion of said mechanical coupling means.

3. A twister-type electromechanical device for converting mechanical energy into electrical energy, comprising: two superimposed plates of dielectric material having a relatively high dielectric constant, each said plate having a remanent polarization in substantially the same direction in the plane of said plate and being effective under the influence of a mechanical shear in the plane of said plate to develop an electric signal field substantially in the plane of said plate normal to said direction of polarization; a center layer of material of relatively low dielectric constant between said plates which is effective to connect said plates mechanically; electrode means, including at least two separate electrodes for each said plate effectively spaced in said signal-field direction along said respective plate, said electrodes for said two plates being effectively interconnected so that potential differences across said electrode means correspond to signal fields, substantially in said planes of said plates between said electrodes, the directions of which are substantially I0 opposite in opposing portions of said two plates, and an undue shunting action between an electrode of one of said plates and an electrode of the other of said plates being obviated by said intervening center layer; mechanical coupling means motion of which is associated with a twisting action of said device involving mechanical shears of opposite senses in said two plates as constrained by said center layer; and means for applying mechanical energy to said mechanical coupling means to provide said motion thereof with said associated twisting action, whereby such applied mechanical energy is converted into said potential differences across said electrode means.

4. A twister-type electromechanical device, comprising: two superimposed plates of barium titanate ceramic material having a relatively high dielectric constant, each said plate having a remanent polarization in substantially the same direction in the plane of'said plate and a mutual coupling action as between an electric signal field substantially in the plane of said plate normal to said direction of polarization and amechanical shear substantially in the plane of said plate; a center layer of material of relatively low dielectric constant between said plates which is effective to connect said plates mechanically; electrode means, including at least two separate electrodes for each of said plates effectively spaced in said signal-field direction along said respective plate, said electrodesfor said two plates being effectively interconnected so that potential differences across said electrode means correspond to signal fields, substantially in said planes ofsaid plates between said electrodes, the directions of which are substantially opposite in opposing portions of said two plates, and an undue shunting action between an electrode of one of said plates and an electrode of the other of said plates being obviated by said intervening center layer; and mechanical coupling means motion of which is associated with a twisting action of said device involving mechanical shears of opposite senses in said two plates as constrained by said center layer; whereby any application of electrical energy to said electrode means to provide said potential differences thereacross causes said motion associated with said twisting action while any movement of said: mechanical coupling means to provide said twisting action causes development of said potential differences across said electrode means.

5'. A twister-type electromechanical device, comprising: two superimposed plates of permanently polarizable titanate-type polycrystalline ceramic material having a relatively high dielectric: constant, each said plate having a remanent polarization in substantially the same direction in the. plane of said plate and a mutual coupling action as between an electric signal field substantially in the plane of said. plate normal to said' direction. ofpolariz-ation and a mechanical shear substantially in the. plane of said; plate; a center layer of material of relatively low dielectric constant between said plates which is effective to connect said plates mechanically; electrode means, including at least two separate electrodes for each of said plates effectively spaced in said signal-field direction along said respective plate, said electrodes for said two plates being effectively interconnected so that potential differences across said electrode means correspond to signal fields, substantially in said planes of said plates between said electrodes, the directions of which are substantially opposite in opposing portions of said two plates, and an undue shunting action between an electrode of one of said plates and an electrode of the other of said plates being obviated by said intervening center layer; and mechanical coupling means motion of which is associated with a twisting action of said device involving mechanical shears of opposite senses in said two plates as constrained by said center layer; whereby any application of electrical energy to said electrode means to provide said potential differences thereacross causes said motion associated with said twisting action while any movement of said mechanical coupling means to provide said twisting action causes development of said potential differences across said electrode means.

6. A twister-type electromechanical device, comprising: two superimposed plates of ceramic dielectric material having a relatively high dielectric constant, each said plate having a remanent polarization in substantially the same direction in the plane of said plate and a mutual coupling action as between an electric signal field substantially in the plane of said plate normal to said direction of polarization and a mechanical shear substantially in the plane of said plate; a center layer of ceramic material of relatively low dielectric constant between said plates which effectively provides a ceramic bond therebetween to connect said plates mechanically in a unitary structure; electrode means, including at least two separate electrodes for each of said plates eifectively spaced in said signal-field direction along said respective plate, said electrodes for said two plates being efiectively interconnected so that potential differences across said electrode means correspond to signal fields, substantially in said planes of said plates between said electrodes, the directions of which are substantially opposite in opposing portions of said two plates, and an undue shunting action between an electrode of one of said plates and an electrode of the other of said plates being obviated by said intervening center layer; and mechanical coupling means motion of which is associated with a twisting action of said device involving mechanical shears of opposite senses in said two plates as constrained by said center layer; whereby any application of electrical energy to said electrode means to provide said potential differences thereacross causes said motion associated with said twisting action while any movement of said mechanical coupling means to provide said twisting action causes development of said potential dilferences across said electrode means.

7. A twister-type electromechanical device, comprising: two rectangular superimposed plates of dielectric material having a relatively high dielectric constant, each said plate having a remanent polarization in substantially the same direction and substantially parallel with two of the sides of said plate and having a mutual coupling action as between an electric signal field substantially in the plane of said plate but substantially normal to said direction of polarization and a mechanical shear substantially in the plane of said plate; a center layer of material of relatively low dielectric constant between said plates which is effective to connect said plates mechanically; electrode means, including at least two separate electrodes for each of said plates effectively spaced in said signal-field direction along said respective plate, said electrodes for said two plates being effectively interconnected so that potential differences across said electrode means correspond to signal fields, substantially in said planes of said plates between said electrodes, the directions of which are substantially opposite in opposing portions of said two plates, and an undue shunting action between an electrode of one of said plates and an electrode of the other of said plates being obviated by said intervening center layer; and mechanical coupling means motion of which is associated with a twisting action of said device involving mechanical shears of opposite senses in said two plates as constrained by said center layer; whereby any application of electrical energy to said electrode means to provide said potential difierences thereacross causes said motion associated with said twisting action while any movement of said mechanical coupling means to provide said twisting action causes development of said potential diiferences across said electrode means.

8. A twister-type electromechanical device in accordance with claim 1, in which the ratio of the elastic moduli of said material of said plates and said material of said center layer is between one half and two; in which the capacitance of said device which would be obtained if said electrodes were interconnected with all of said electrodes for one of said plates connected together and with all of said electrodes for the other of said plates connected together is much smaller than the capacitance of said device which would be obtained if said several electrodes were interconnected as if to apply electric signal fields which are substantially in said planes of said plates between said electrodes but the directions of which are substantially the same in opposing portions of said two plates; in which the length of said plates in said direction of said remanent polarization is at least twice as great as the width of said plates in said signal-field direction; in which the over-all thickness of said two plates and said center layer is of the order of twice as great as the thickness of said center layer alone; in which said width of said plates is at least two and one half times as great as said over-all thickness; and in which the extent of said electrode means for one of said plates, when measured in said signal-field direction from an edge of said plate to the midpoint of the widthwise dimension thereof, is related to said over-all thickness dimension by a ratio within the range of 0.6 and 0.8.

References Cited in the file of this patent UNITED STATES PATENTS 1,798,101 Nicolson Mar. 24, 1931 2,486,560 Gray Nov. 1, 1949 2,540,194 Ellett Feb. 6, 1951 2,625,663 Howatt Jan. 13, 1953 FOREIGN PATENTS 121,324 Austria Feb. 10, 1931 907,492 France Mar. 13, 1946 924,079 France July 25, 1947 

